The invention finds applications in the automotive field, and more precisely in the field of the projection of light for motor vehicles. In particular, it is applicable for the fastening of a light source with a possibility of interchangeability between light sources of different types.
At the present time, apparatuses for projecting light (or headlights) for motor vehicles are provided with light sources which may be of different kinds. In particular, front headlights of vehicles are equipped with light sources which may be of two different kinds, namely: a first kind with a halogen bulb, and a second kind with a discharge bulb. In the second case, the light source is also equipped with a high tension module which provides the electrical power supply for the discharge bulb.
Among light sources with discharge bulbs, there currently exist two types of light sources which are called a D1 lamp and D2 lamp. Each of these light sources or lamps comprises a discharge bulb, a bulb base and a high tension module. The high tension module is fixed non-removably in the case of a D1 lamp, while on the other hand, it is removable in the case of a D2 lamp. In other words, in the case of a D1 lamp, the high tension module is an integral part of the lamp. In a D2 lamp, the high tension module is not incorporated in the lamp; it consists of an independent component which is removably mounted on the lamp.
One example of a D1 lamp is shown in FIG. 1. This Figure shows a light source 1 comprising a discharge bulb 2, a bulb foot 4 and a high tension module 3. The bulb 2 is fixed securely to the module 3 in the region of the bulb base 4. An optical reflector 5 is formed with a passage hole 6 at the level of a skirt portion 7. The bulb 2 passes through the hole 6. A body 2a of the bulb 2 is mounted inside the reflector 5. The bulb base 4 is situated on the outside of the reflector 5. In the D1 lamp assembly shown in FIG. 1, a lamp holder 8, which may for example be of cylindrical circular shape, is an integral part of the reflector 5. The lamp holder 8 and reflector 5 together constitute a single and common component 9, which is referred to as the counterpart of the headlight. The purpose of the lamp holder 8 is to support the discharge bulb 2. It also centres and orientates the discharge bulb 2 inside the reflector 5.
The lamp holder 2 may also be a member separate from the reflector 5. The lamp holder 2 is then not an integral part of the reflector; it is fixed firmly to the reflector during assembly of the headlight. In this case too, the lamp holder 8 and the reflector constitute the counterpart of the headlight.
In the D1 lamp assembly, the discharge bulb 2 is fitted on a high tension module 3 which is fixed to the said bulb. The module 3 has a substantially square outside contour, and is of relatively small size as compared with a D2 lamp and its module which will be described later herein. However, the fact that the module 3 is not removable gives rise to certain disadvantages. In this connection, when a user wants to change the discharge bulb in a headlight of his vehicle, for example because it is faulty, he is obliged to change the whole assembly consisting of the bulb and high tension module. In addition, changing of this bulb and high tension module assembly is a relatively delicate operation, firstly due to the difficulty of access to the D1 lamp and operations that have to be carried out in order to withdraw the faulty assembly and install a new assembly, and secondly due to the risks inherent in the high voltage present in the module. The user is therefore obliged to have the unit changed by a professional, which involves not only the cost of the unit but also a labour charge.
One example of a D2 lamp with its high tension module is shown in FIG. 2. FIG. 2 shows a light source 11 which comprises a discharge bulb 12.
A high tension electrical module 13 is fixed removably on the bulb 12 in the region of a bulb base 14. A reflector 15 is formed with a passage hole 16 close to the skirt portion 17, to allow the bulb 12 to pass through. The body 12a of the bulb 12 is mounted inside the reflector 15. The bulb base 14 is situated on the outside of the reflector 15. As for the D1 lamp, the D2 lamp includes a lamp holder 18, which is for example of circular cylindrical form and which may be an integral part of the reflector 15 or, alternatively, a separate component fixed to the reflector 15. The lamp holder 18 and reflector 15 together constitute the counterpart 19 of the headlight.
In the D2 lamp assembly, the bulb has no associated electronic circuitry, that is to say the high tension module is independent of the bulb. In other words, the high tension module is not an integral part of the discharge bulb: it is fixed on the bulb after the bulb has been fitted in the reflector. It is therefore possible, during fitting and removal of the headlight, to disconnect the high tension module from the bulb. This has a certain advantage as compared with the D1 lamp. In this connection, with a D2 lamp when the lamp is faulty, it is possible to change only the bulb and to preserve the initial high tension module. However, changing of a bulb in a D2 lamp is even more delicate than the changing of the bulb and module unit with a D1 lamp. In this connection, not forgetting the difficulty of access which is inherent in a headlight, the user first has to extract the module and withdraw the bulb; he then has to change the bulb and replace the module on the bulb, with all the risks inherent in the high voltage in the module. The user is therefore obliged to get a professional to change the bulb.
At the present time, arrangements are known for fixing a bulb on a counterpart with a D2 lamp. One example of such an arrangement is a closed sleeve. With this closed sleeve, the high tension module is first fixed to the discharge bulb, and then the discharge bulb is mounted in the reflector. The sleeve is then brought into the fastening zone. For this purpose, the high tension module is slid in the sleeve into the fastening zone. The sleeve is then secured to the reflector with a bayonet fitting. Such a fastening sleeve is not well adapted for a D1 light source. In this connection, either the square outer contour of the high tension module in the D1 light source prevents its introduction into the closed sleeve, or else the sleeve would have to have too large a diameter to enable the light source to be fixed on the counterpart subsequently.
It is therefore impossible, with such apparatus, to interchange the two lamps, the D1 and the D2. In other words, a user whose vehicle has a D2 light source cannot later, for cost and availability reasons, introduce a D1 light source into his light projecting apparatus, and vice versa.
There also exist spring fastening systems which are adapted either for D1 lamps or for D2 lamps, but without any possibility of these two types of lamps being interchanged, for reasons of geometry and size.
Motor vehicle headlights also exist which have lamp locking systems which enable several standard types of lamps to be locked in place. Such a system is described for example in Application EP-A-1 108 950.
However, such a system is not well adapted for light sources with discharge bulbs. In this connection, this type of light source with a discharge bulb, connected to a high tension module, must include means which give electrical continuity on the one hand, and screening on the other, in order to avoid leakage from the electromagnetic field. In this connection, in this type of light source, because of the generation of a high voltage by the high tension module, the headlight is subjected to numerous electromagnetic radiations. In order to avoid propagation of the electromagnetic radiation within the vehicle, it is necessary to screen the light projecting apparatus. As to this, the electromagnetic radiations may give rise to numerous disturbances in the electrical assembly of the vehicle. Since a number of functions in a modern motor vehicle are managed by an electronic system, these electromagnetic disturbances may have serious consequences.
The main object of the invention is to overcome the drawbacks of the techniques discussed above, and to enable a bulb to be fixed on a headlight counterpart, with the same fastening system for a D1 lamp as for a D2 lamp. To this end, the invention proposes a fastening system for fixing a light source with a discharge bulb which is adaptable for different types of light sources. This system is particularly well adapted for light sources with discharge bulbs, such as D1 and D2 lamps, because it enables electrical continuity and electromagnetic screening to be ensured in order to avoid leakage of electromagnetic fields into the inside of the vehicle.